@article {Castillo071886, author = {Dean M. Castillo and Leonie C. Moyle}, title = {Reinforcement of conspecific sperm precedence weakens sexual selection in sympatric populations of Drosophila}, elocation-id = {071886}, year = {2017}, doi = {10.1101/071886}, publisher = {Cold Spring Harbor Laboratory}, abstract = {Sexual selection is well recognized as a driver of reproductive isolation between lineages, however selection for increased reproductive isolation could also reciprocally feed back to alter sexual selection, when these processes share a genetic basis. Direct selection for isolation is most likely to occur in the context of {\textquoteleft}reinforcement{\textquoteright}, where selection acts to increase prezygotic barriers to reduce the cost of heterospecific matings. Many studies of reinforcement focus on premating reproductive barriers, however postmating traits--such as conspecific sperm precedence (CSP)--can also respond to reinforcing selection. When CSP and intrapopulation sperm competition (ISC) share a genetic basis, selection for increased CSP in sympatric populations could alter ISC and the strength of sexual selection. We tested this prediction with the sister species Drosophila pseudoobscura and D. persimilis, using two sympatric and two allopatric populations of D. pseudoobscura. We used a factorial sperm competition experiment to evaluate differences in CSP and ISC between sympatric and allopatric populations. Using multiple tester males across this factorial design also allowed us to estimate the opportunity for sexual selection within each population. Consistent with a pattern of reinforcement, the sympatric populations had higher mean CSP. Reinforcement, in turn, decreased the average offensive sperm competitive ability specifically within these sympatric populations, allowing less opportunity for sexual selection to operate among conspecific males. These data demonstrate that strong reinforcing selection for reproductive isolation can have consequences for sexual selection and sexual interactions within species, in these important postmating sperm competition traits.SIGNIFICANCE STATEMENT Sexual selection can accelerate speciation by driving the evolution of reproductive isolation, but forces driving speciation could also reciprocally feedback on sexual selection. Using assays of sperm competition within and between two sister species, we show that populations of Drosophila pseudoobscura that co-occur with sister species D. persimilis have an elevated ability to outcompete heterospecific sperm, a signature of direct selection to increase reproductive isolation where these species interact. We also find these D. pseudoobscura populations have decreased sperm competitive ability against conspecific males. Our findings demonstrate that direct selection to increase reproductive isolation against other species can reduce the opportunity for sexual selection within species, a collateral effect of reproductive traits responding to heterospecific interactions.}, URL = {https://www.biorxiv.org/content/early/2017/06/01/071886}, eprint = {https://www.biorxiv.org/content/early/2017/06/01/071886.full.pdf}, journal = {bioRxiv} }